This invention relates to novel derivatized, crosslinked, and derivatized and crosslinked polysaccharide graft polymers.
Oxidative and non-oxidative methods have been used to introduce aldehyde groups into polysaccharides such as starches, gums, and celluloses. The oxidative methods used have included treatment with periodic acid, periodates, alkali metal ferrates, and alkali metal bromites or hypobromites. See U.S. Pat. No. 3,086,969 (issued Apr. 23, 1963 to J. E. Slager), U.S. Pat. No. 3,062,652 (issued Nov. 6, 1962 to R. A. Jeffreys et al.), U.S. Pat. No. 3,632,802 (issued Jan. 4, 1972 to J. N. BeMiller et al.), and U.S. Pat. No. 3,553,193 (issued Jan. 5, 1973 to D. H. LeRoy et al.). The disadvantages of the oxidative method include degradation to lower molecular weight products and the formation of carboxyl groups due to further oxidation of the aldehyde groups. The presence of carboxylic groups in aldehyde starches has several disadvantages in addition to the obvious reduction in the degree of aldehyde substitution. These include the introduction of hydrophilic properties due to the carboxyl groups, an upset in the cationic/anionic ratio when a cationic starch base is used and the possible formation of salts which could give rise to ionic crosslinking.
The non-oxidative methods typically involve the reaction of the polysaccharide with an aldehyde-containing reagent. See U.S. Pat. No. 3,519,628 (issued July 7, 1970 to S. M. Parmerter), U.S. Pat. No. 3,740,391 (issued June 19, 1973 to L. L. Williams et al.) and U.S. Pat. No. 2,803,558 (issued Aug. 20, 1957 to G. D. Fronmuller). The starch derivative of Parmerter is prepared by reaction with an unsaturated aldehyde (e.g., acrolein) and has the structure Starch-O--CH(R.sup.1)--CH(R.sup.2)--CHO where R.sup.1 and R.sup.2 are hydrogen, lower alkyls or halogen. The starch derivative of Williams is prepared by reaction with acrylamide followed by reaction with glyoxal. The gum derivative of Fronmuller is prepared by treating the dry gum (e.g., locust bean or guar gum) with peracetic acid to reduce the viscosity, neutralizing, and then reacting with glyoxal. Water-soluble cellulose ethers (e.g., hydroxyethylcellulose) have been reacted with glyoxal or ureaformaldehyde to give aldehyde-containing derivatives.
One of the disadvantages of introducing the aldehyde groups directly using an aldehyde-containing reagent is the possibility of the derivative crosslinking prior to use.
The major uses for dialdehyde starches reflect the reactive nature of the polymeric polyaldehyde in crosslinking substrates containing amino, hydroxyl and imino groups. See Japan Kokai 57-202,263 (published Dec. 11, 1982, Hohnen Oil Co., Ltd., C.A. 98: 200152m 1983) which discloses a water-resistant aqueous adhesive containing dialdehyde starch and a compound containing two or more isocyanate groups (e.g., polymethylenepolyphenylene polyisocyanate). See U.S. Pat. No. 3,706,633 (issued Dec. 19, 1972 to E. Katchalski et al.) which discloses the crosslinking of dialdehyde starch with an alkylene diamine (e.g., hexamethylene diamine or methylene dianiline) to form a highly crosslinked product. However, the crosslinking cannot be controlled because the granular dialdehyde starch is reactive toward the starch hydroxyls, thus leading to premature self-crosslinking rather than crosslinking via the diisocyanate or diamine.
Aldehyde-containing synthetic heteropolysaccharides are disclosed in U.S. Pat. No. 4,663,448 (issued May 5, 1987 to Chung-Wai Chiu). They have the structure R'--O--A--O--Starch where A is --CH.sub.2 --CH.sub.2 -- or --CH.sub.2 --CH(OH)--CH.sub.2 --, Starch-O represents a starch molecule, and R' is ##STR1## which represents a hexose containing a galactose configuration. A is attached to the hexose by an acetal linkage and to the starch by an ether linkage. Acetal- and aldehyde-containing polysaccharides are disclosed in U.S. Pat. No. 4,675,394 (issued June 23, 1987 to Daniel B. Solarek et al.), U.S. Pat. No. 4,731,162 (issued Mar. 15, 1988 to Daniel B. Solarek et al.), U.S. Pat. No. 4,741,804 (issued May 3, 1988 to Daniel B. Solarek et al.), U.S. Pat. No. 4,749,800 (issued June 7, 1988 to Patrick G. Jobe et al.), U.S. Pat. No. 4,788,280 (issued Nov. 29, 1988 to Robert L. Billmers et al.), U.S. Pat. No. 4,801,699 (issued Jan. 3, 1989 to Robert L. Billmers et al.), U.S. Pat. No. 4,804,769 (issued Feb. 14, 1989 to Martin M. Tessler et al.), and U.S. Pat. No. 4,839,449 (issued June 13, 1989 to Robert L. Billmers et al.).
Polysaccharide graft polymers containing acetal and aldehyde groups are disclosed in U.S. Pat. No. 4,860,151 issued June 13, 1989 in the name of John J. Tsai et al.
These acetal-containing products, both the derivatives and graft polymers, have been shown to possess some very unique properties. Once the polysaccharide is dispersed and the acetal is converted to aldehyde by lowering the pH to less than 7, crosslinking can occur between the aldehyde and any available hydroxyl group.
There is always a need for new derivatized Polysaccharides and crosslinked polysaccharides, particularly polysaccharide which will crosslink when desired.